1. Field of the Invention
The subject invention relates generally to a steering column assembly for a vehicle, and more specifically to a steering column assembly collapsible along a longitudinal axis in response to a collision event.
2. Description of the Prior Art
Automotive steering column assemblies are typically equipped with kinetic energy absorption devices. The energy absorption devices reduce injury to a vehicle operator caused by the operator impacting a steering wheel as a result of a collision event. Such impacts during vehicle collision typically cause the steering column assemblies to collapse. The energy absorption devices absorb the energy transmitted through the steering column assembly as the steering column assembly collapses.
Such energy absorbing steering columns generally include a lower jacket disposed within an upper jacket. A bushing is disposed between the upper jacket and the lower jacket to de-lash the steering column assembly, with the bushing being coupled to the upper jacket. The upper jacket and the bushing translate linearly through a collapse stroke during the collision event. A load, i.e. a force, generated by the driver impacting the steering wheel initiates the collapse stroke. The steering wheel housing moves against a resisting or reactive force that may be produced by the energy absorption device designed to convert a portion of the driver's kinetic energy into work. The resisting force may be generated by systems including a plastically deformable metal element that is a part of the energy absorbing device.
During the collision event, the load is applied to the steering column assembly, with a horizontal component of the load being applied longitudinally to the steering column assembly and a vertical component of the load being applied vertically to the steering column assembly, i.e., transverse to the steering column assembly. The vertical component of the load creates a bending moment in the upper jacket, which is transferred to the lower jacket by the bushing. Accordingly, a resultant force is created between the upper jacket and the lower jacket to resist the bending moment. Typically, a first resultant force is located near a forward end (nearer the front of the vehicle) of the bushing and is directed downward, and a second resultant force is located near a rearward end (nearer the rear of the vehicle) of the bushing and is directed upward. The first resultant force and the second resultant force increase the frictional sliding force between the bushing and the lower jacket as the upper jacket and the bushing slide relative to the lower jacket during the collision event. The increased frictional sliding force negatively affects the performance of the energy absorption device.